Easy to install automatic pressure-control device works with many
different types of irrigation systems and can help reduce erosion on
slopes.

A new device automatically blocks unwanted surges in water pressure
throughout farm irrigation networks, yet is simpler to use and less
costly than some other options.

The apparatus, says agricultural engineer Dennis C. Kincaid, keeps
pressure to within 10 percent of the target level. This precision helps
ensure that thirsty plants growing on steep slopes are watered
uniformly. Too, the device helps growers avoid the overirrigation that
could otherwise trigger soil erosion and accelerate leaching of farm
chemicals into underground water supplies.

Growers can use the lightweight, low-maintenance apparatus with a
variety of irrigation systems, including surface or buried drip and
lateral-move or center-pivot sprinkler. And the device can be easily
spliced into existing setups, according to Kincaid. He is with the ARS
Northwest Irrigation and Soils Research Laboratory at Kimberly, Idaho.

The components, Kincaid says, are inexpensive, readily available, and
easy to adjust. They include a butterfly valve or similar disk, a metal
plate that acts as a lever, a small air cylinder actuator that serves as
the hydraulics assembly, a simple external tension spring that works
alongside the air cylinder, and a length of flexible tubing.

Kincaid estimates that about 11 million acres of irrigated farmland
in the United States are hilly enough - with slopes of 5 percent or
more, for example - to warrant pressure control valves. He admits that
the idea of using manually operated butterfly valves to do this task
isn't new. But the automatic control system that he devised and
that ARS has now patented is unique.

In brief, the butterfly valve in the irrigation pipe is connected to
the metal plate or lever outside the pipe. The external tension spring
and air cylinder are aligned, at their base, to connect with the pipe.
At their other end, they are bolted to the metal plate at two different
positions, using holes pre-drilled into the plate for this purpose. The
flexible tube transmits pressure from the irrigation pipe to the base of
the cylinder.

At the proper initial setting, the spring and cylinder are retracted
and the butterfly valve opens. The spring's tension will keep the
valve open and resist the cylinder's force when pressure downstream
of the valve is at or below the level the grower selects.

When the downstream pressure exceeds the target, however, the
resulting pressure in the flexible tubing will force the cylinder to
overcome the spring's tension. The spring and cylinder extend,
moving the metal lever and causing the butterfly valve to close. As the
pressure decreases, the spring and cylinder contract to their starting
positions, causing the lever to shift and the butterfly valve to open.

Building upon earlier work by Kimberly colleague Allan S. Humpherys,
Kincaid compiled a series of standard mathematical equations, that
irrigation system designers or valve manufacturers can use to determine
the correct size of the spring and cylinder, as well as the correct
angles or settings to use when bolting these components to the lever. Or
they can do the calculations on a computer using the spreadsheet program
that Kincaid and coworker David G. Romspert have prepared.

Units would cost about $100 to $150 each, depending on pipe diameter
and other factors, Kincaid estimates. He says the device is suitable for
pipes or conduits that measure 2 to 12 inches in diameter, carry flows
of 25 to 2,500 gallons per minute, and handle pressures of 5 to 90
pounds per square inch.